public class DoubleLinkedList {
    public ListNode head = new ListNode(-1);
    public ListNode last;
    //带头
    public void display(){
        if (this.head.next==null){
            return;
        }
        ListNode head1 = this.head.next;
        ListNode cur = head1;
        while (cur != null){
            System.out.print(cur.val+"");
            cur = cur.next;
        }
        System.out.println();
    }
    //不带头
//    public void display(){
//        ListNode cur = this.head;
//        while (cur != null){
//            System.out.print(cur.val+"");
//            cur = cur.next;
//        }
//        System.out.println();
//    }
    public int size(){
        if (this.head.next==null)
            return 0;
        int count = 0;
        ListNode cur = this.head.next;
        while (cur != null){
            count++;
            cur = cur.next;
        }
        return count;

    }
    //查找是否包含关键字key在单链表中
    public boolean contains(int key){
        if (this.head.next==null)
            return false;
        ListNode cur = this.head.next;
        while (cur != null) {
            if (cur.val == key) {
                return true;
            }
            cur = cur.next;
        }
        return false;
    }
    //头插法
    public void addFirst(int data){
        ListNode node = new ListNode(data);
        if (this.head.next == null){
            this.head.next = node;
            node.prev = head;
            this.last = node;
        }else {
            node.next = this.head.next;
            node.prev = this.head;
            this.head.next = node;
        }
    }
    //尾插法
    public void addLast(int data) {
        ListNode node = new ListNode(data);
        if(this.head.next == null){
            this.head.next = node;
            node.prev = head;
            this.last = node;
            return;
        }
        this.last.next = node;
        node.prev = this.last;
        this.last = node;
    }

    //任意位置插入
    public void addIndex(int index,int data){
        if (index < 0 || index >size()){
            System.out.println("index 位置不合法");
            return;
        }
        ListNode node = new ListNode(data);
        if (index == 0){
            addFirst(data);
            return;
        }
        if (index == size()){
            addLast(data);
            return;
        }
        ListNode cur = searchIndex(index);
        node.next = cur;
        node.prev = cur.prev;
        cur.prev.next = node;
        cur.prev = node;
    }
    public ListNode searchIndex (int index){
        ListNode cur = this.head.next;
        while (index != 0){
            cur = cur.next;
            index--;
        }
        return cur;
    }
}
class ListNode{
    public int val;
    public ListNode prev;
    public ListNode next;
    public ListNode(int val){
        this.val = val;
    }
}